Abstract Viruses engineered for gene therapy and the destruction of tumor cells (oncolytic viruses) are a growing medical market (~$1B by 2026) with profound implications for human health. To comply with FDA regulations, most drug products remove microbial contaminants with sterile filtration as a final step. In the case of viruses, the broad pore sizes and high internal surface areas of commercial sterile filtration membranes result in massive product loss (~80%). Consequently, GMP paradigms for the production of medical grade virus must implement aseptic practices at every step of production. SiMPore uses silicon-based manufacturing to create ultrathin (~100-400 nm thick) membranes with precision pore sizes and more than 3 orders-of-magnitude less internal surface area than conventional sterile-filters. This proposal investigates the hypothesis that these distinctive properties will enable sterile filtration of virus with less than 10% loss. In Aim 1 we will develop and characterize ultrathin membranes with a high density of 0.2 m slit-pores. This pore size matches the average pore size of commercial sterile filters, but with a dramatic reduction in thickness and internal surface area. Functional characterization will include sieving, burst pressures, and hydraulic permeability testing. In Aim 2, we will evaluate SiMPore membranes as sterile filters by comparing loss and capacity directly to 3 commercial sterile membrane filters. With success in Phase I, SiMPore's membranes will be scaled up from chip-based to sheet-based formats and used in diafiltration modules as final processing step in actual viral manufacturing processes during Phase II.